Citigroup, HSBC are among firms targeted by regulators, according to people close to the probe

American banks have so far escaped the billions of dollars in fines that have been levied by U.S. and British regulators leading a global seven-year probe into interest-rate rigging. That is likely to change.

The U.S. Commodity Futures Trading Commission and the U.K. Financial Conduct Authority are working on a final round of civil charges against several banks for alleged manipulation of a benchmark underpinning interest rates on trillions of dollars of financial contracts world-wide, according to people close to the probe....